The structural basis of lipid scrambling and inactivation in the endoplasmic reticulum scramblase TMEM16K

Simon R. Bushell, Ashley C.W. Pike, Maria E. Falzone, Nils J. G. Rorsman, Chau M, Ta, Robin A. Corey, Thomas D. Newport, Chitra A. Shintre, Annamaria Tessitore, Amy Chu, Qinrui Wang, Leela Shrestha, Shubhashish M.M. Mukhopadhyay, James D. Love, Nicola A. Burgess-Brown, Rebecca Sitsapesan, Phillip J. Stansfeld, Juha T. Huiskonen, Paolo Tammaro, Alessio Accardi, Elisabeth P. Carpenter

Oct 22, 2018
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Received Date: 14th October 18

Membranes in cells have defined distributions of lipids in each leaflet, controlled by lipid scramblases and flip/floppases. However, for some intracellular membranes such as the endoplasmic reticulum the scramblases have not been identified. Members of the TMEM16 family have either lipid scramblase and ion channel activity, or specific chloride channel activity. Although TMEM16K is widely distributed and associated with the neurological disorder autosomal recessive spinocerebellar ataxia type 10 (SCAR10), its location in cells, function and structure are largely uncharacterised. Here we show that TMEM16K is an ER-resident calcium-regulated lipid scramblase. Our crystal structures of TMEM16K show a scramblase fold, with an open lipid transporting groove. Additional structures solved by cryo-EM reveal extensive conformational changes extending from the cytoplasmic to the ER side of the membrane, giving a state with a closed lipid permeation pathway. Molecular dynamics simulations showed that the open-groove conformation is necessary for scramblase activity. Our results suggest mechanisms by which missense variants of TMEM16K could cause SCAR10 ataxia, providing new hypotheses to explore for therapy.

Read in full at bioRxiv.

This is an abstract of a preprint hosted on an independent third party site. It has not been peer reviewed but is currently under consideration at Nature Communications.

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